The present invention relates to an air valve device for a motor vehicle, comprising an air valve support with a flow opening and with at least one air valve extending into or passing through the flow opening, and which is movably seated on the air valve support between a blocking position as one working position, and a flow position as another working position, wherein the air valve in the blocking position provides a greater resistance to a particular flow through the flow opening than in the flow position, wherein the air valve device further comprises a drive device which is connected to the at least one air valve as movement drive for movement between its working positions at least temporarily in a drive force transmitting manner, and wherein the air valve device features a control device to actuate the drive device.
An air valve device of this kind is generally known. They are normally located on the front side of motor vehicles in order to change the flow of air through the flow opening into the engine compartment during the forward movement of the motor vehicle. The passage of air through the flow opening is adjustable by movement of the air valves between their working positions, in particular as a function of the operating parameters of the vehicle.
In this way, by selecting the working position of the air valves, the convective cooling of the functional aggregates of the motor vehicle located in the direction of flow behind the flow opening can be changed. By operation of the motor vehicle after a cold start with the air valves in the blocking position, for example, a convective cooling of the internal combustion engine in the engine compartment of the motor vehicle can be prevented or restricted, so that it can warm up more quickly to its rated operating temperature, in which it emits less pollution compared to the transient, cold-start state. To protect against overheating of the internal combustion engine, the air valves can be adjusted into the flow position, so that the internal combustion engine or other functional aggregates of the motor vehicle can be cooled by convection by the air flowing through the flow opening.
Air valves are often located around a pivot axis positioned in parallel to their longitudinal axis so as to pivot on the air valve support. The air valves are then designed as large-area components having their greatest dimension along the pivot axis and having their minimum dimension as a thickness dimension orthogonal to the pivot axis.
An additional dimension, the width dimension, which proceeds both orthogonal to the thickness dimension and also orthogonal to the longitudinal dimension, denotes the spacing between the two longitudinal edges of the air valve. Vehicle manufacturers usually endeavor to change the effective flow cross-section of a particular flow opening with as few air valves as possible, in order to obtain the largest possible flowable cross-section when the air valves are left in the flow position.
However, the smallest number of air valves means a large width of the air valves, due to the structure of the flow opening.
Even though the present invention pertains to the change of position of at least one air valve into a target position range predetermined to be less potentially harmful in an assumed collision event, for the purpose of a simplified explanation, quadrilateral air valves are assumed whose thickness is much smaller than their width and in turn, their width is much smaller than their length. Using a simplified, but accurate assumption, the air valve is arranged with its longitudinal axis parallel to the lateral axis of its supporting vehicle and can pivot between its working positions about a pivot axis parallel to the vehicle lateral axis or to the air valve longitudinal axis. It is further assumed that the width direction of the air valve in its blocking position is oriented parallel to the vehicle yaw axis and in its flow position is parallel to the vehicle roll axis. Alternatively, the air valve—depending on vehicle type—can pivot around a pivot axis parallel to the vehicle yaw axis, and in turn, the air valve longitudinal axis is parallel to the pivot axis of the air valve. Then in the latter case, in contrast to the foregoing it is assumed that the width direction of the air valve in its blocking position is oriented parallel to the vehicle lateral axis and in its flow position is in turn parallel to the vehicle roll axis.
If the vehicle equipped with one such air valve device on its front side impacts frontally against an obstacle not extending across the entire width of the vehicle, such as against a person, a majority of the collision-related stress on the air valve is a flexural stress about a flexure axis parallel to the vehicle yaw axis.
The resistance that the at least one air valve applies against one such flexure, depends on its area moment of inertia. The area moment of inertia of a body with a square cross-section with height h and thickness d under a flexure about a lateral axis parallel to the thickness direction, is proportional to the product of the thickness times the third power of the height.
Then if the vehicle impacts frontally against a person with the at least one air valve in the flow position, as assumed in the above simplification, the lateral axis of the lateral stress of the air valve runs approximately in the thickness direction, so that the area moment of inertia of the air valve is proportional to the product of the thickness of the air valve and the third power of its width. In order to attain the most “flexural” and thus the least damaging impact of the air valve upon a person in the case of such a collision, it is thus advisable to reduce the width of the air valve since it is proportional to the third power of the flexural deformation resistance of the air valve. From this, a requirement is derived for the narrowest possible air valve and consequently also for the greatest possible number of air valves. An accident involving a person, and an injury to the person involved in an accident, are only one of many possibilities. The air valves oriented in the flow position with their width dimension essentially longitudinal to the vehicle roll axis, also represent an increased risk of damage, due to their large flexural resistance, to functional components located immediately behind them, such as a coolant heat exchanger.
There is thus, with a view toward the most effective convective cooling, a requirement that there be as few air valves as possible, which would be, however, as wide as possible and the opposing requirement for the least injurious, and thus the narrowest possible valves, which would then have to be provided in the largest possible number. These diametrically opposed target requirements cannot be reconciled and cannot be realized simultaneously in one vehicle.